The proposed research seeks to use integrated photoacoustic imaging and ultrasound, combined with molecularly targeted contrast agents, to acquire non-invasive in vivo molecular images of tumor cell receptor expression. While methods of molecular imaging have been developed, challenges with spatial resolution, depth of field, temporal resolution and sensitivity remain. Multimodal photoacoustic and ultrasound imaging combines advantageous features of optical and ultrasound imaging, enabling optical probing of contrast at a high resolution at a depth of several centimeters in vivo. The proposed research seeks to demonstrate photoacoustic molecular imaging of tumor receptor expression. The hypothesis is that photoacoustic imaging with multiplex targeted contrast agents, combined with high resolution ultrasound imaging, will provide the necessary sensitivity and resolution to detect and distinguish between regions of in vivo tumors which are expressing different receptors. The first aim of the project is to demonstrate in vitro photoacoustic imaging of multiplex targeted contrast agents which have been endocytosed in cells expressing the relevant receptor. Inclusions containing targeted cells will then be injected in ex vivo animal tissue and imaged using multispectral photoacoustics in order to develop statistical correlations to distinguish between contrast agents with varying optical properties, and native tissue chromophores. The second aim will demonstrate in vivo photoacoustic and ultrasound imaging of complex tumor receptor expression within cancer tumor xenografts in murine animal models using injections of the multiplex targeted contrast agents. The third aim will perform longitudinal studies on tumor growth and response to drug treatment within the murine model, using the combined photoacoustic and ultrasound imaging techniques to image targeted contrast agents uptaken within the tumor. The training plan proposed to accomplish these goals has been designed to establish trainee mentors with specific technical expertise. The selected mentors are experts in ultrasound and photoacoustic imaging; the synthesis and applications of plasmonic nanoparticles for biomedical applications; and the cell expression and regulation of cancer; respectively. The PI will enroll in formal training in the ethical conduct of research and in training specific to her research field, to prepare her for independent research.